158 THE PLANT IN ACTION. [LESSON 26. 



into something upon which they can live, namely, into food. All 

 the food of all animals is produced by plants. Animals live upon 

 vegetables; and vegetables live upon earth and air, principally 

 upon the air. 



447. Plants feed npon Earth and Air. This is evident enough from 

 the way in which they live. Many plants will flourish in pure sand 

 or powdered chalk, or on the bare face of a rock or wall, watered 

 merely with rain-water. And almost any plant may be made to 

 grow from the seed in pure sand, and increase its weight many times, 

 even if it will not come to perfection. Many naturally live suspended 

 from the branches of trees high in the air, and nourished by it alone, 

 never having any connection with the soil (81); and some which 

 naturally grow on the ground, like the Live-for-ever of the gardens, 

 when pulled up by the roots and hung in the air will often flourish 

 the whole summer long. 



448. It is true that fast-growing plants, or those which produce 

 considerable vegetable matter in one season, especially in such a 

 concentrated form as to be useful as food for man or the higher 

 animals, will come to maturity only in an enriched soil. But 

 what is a rich soil? One which contains decomposing vegetable 

 matter, or some decomposing animal matter ; that is, in either case, 

 some decomposing organic matter formerly produced by plants ; 

 aided by this, grain-bearing and other important vegetables will 

 grow more rapidly and vigorously, and make a greater amount of 

 nourishing matter, than they could if left to do the whole work at 

 once from the beginning. So that in these cases also all the organic 

 matter was made by plants, and made out of earth and air. 



449. Their Chemical Composition shows what Plants are made of, The 

 soil and the air in which plants live, and by which they are every- 

 where surrounded, supply a variety of materials, some likely to be 

 useful to the plant, others not. To know what elements the plant 

 makes use of, we must first know of what its fabric and its products 

 are composed. 



450. We may distinguish two sorts of materials in plants, one of 

 which is absolutely essential, and is the same in all of them ; the 

 other, also to some extent essential, but very variable in different 

 plants, or in the same plant under different circumstances. The 

 former is the organic, the latter the inorganic or earthy materials. 



451. The Earthy or Inorganic Constituents. If we burn thoroughly a 

 leaf, a piece of wood, or any other part of a vegetable, almost all of 



